There is already known for a long time vehicle seats currently used in airplanes, trains or automobile vehicles, these seats comprising a seat back the inclination of which can be adjusted relatively to a seat frame. A plurality of more or less complicated discontinuous mechanisms have already been proposed for adjusting a seat back with respect to a seat frame. However all the known mechanisms have particular drawbacks in that, with a certain time of use, because of the design of the articulation and also because of vibrations to the vehicle, clearances are formed both in the toothing of the members provided for locking the seat back with respect to the seat frame and in the rotation pin mounted between the seat frame and the seat back since the rotation pin is only supported on one point of the bearing member. Therefore, on the one hand, the safety is not properly ensured and, on the other hand, the seat back is not rigidly fixed and provides therefore a bad impression for the seat user.